Hardened silver coated journal bearing surfaces and method

ABSTRACT

An article comprises a metal alloy substrate and a plated wear interface layer disposed over a surface of the metal alloy substrate. The wear interface layer has a chemical composition including between about 0.005 wt % and about 0.050 wt % of antimony (Sb), and the balance silver (Ag) and incidental impurities.

CROSS REFERENCE TO RELATED APPLICATION

This application is a divisional of U.S. application Ser. No. 13/682,006filed Nov. 20, 2012 for “Hardened Silver Coated Journal Bearing Surfacesand Method” by Thomas R. Hanlon, William P. Ogden, and Eli N. Ross.

BACKGROUND

The described subject matter relates to turbine engines, and moreparticularly, to wear interface surfaces for use in turbine engines.

Turbine engines such as those used for aircraft have journal bearings inmultiple locations, including those used to support rotating elementsdisposed in shaft bearing assemblies and fan drive gear systems.Interface surfaces of the journal bearings and the rotating elementsthey support must have sufficient hardness and resiliency to resist weareven under extreme combinations of pressure and velocity. One commonwear interface surface for elements rotating about aircraft journalbearings is a magnetron-sputtered copper-lead alloy with a specializedmicrostructure. The manufacturing process of this alloy is complex andexpensive, requiring specialized equipment.

Similar properties have not been previously available in silver-basedcoatings. Silver has been used previously to provide a low-frictionsurface for various alloys, but standard silver coatings have arelatively short useful life due to limited hardness and resilienceproperties. Thus they have not traditionally been useful for highperformance applications requiring long service life and maintenanceintervals over a wide variety of extreme operating conditions.

SUMMARY

An article comprises a metal alloy substrate and a plated wear interfacelayer disposed over a surface of the metal alloy substrate. The wearinterface layer has a chemical composition including between about 0.005wt % and about 0.050 wt % of antimony (Sb), and the balance silver (Ag)and incidental impurities.

A gear element comprises a gear body, a plurality of gear teethdistributed circumferentially around the gear body, and a plated wearinterface layer. The wear interface layer is disposed over an inwardlyfacing gear surface. The wear interface layer has a chemical compositionincluding between about 0.005 wt % and about 0.050 wt % of antimony(Sb), with the balance silver (Ag) and incidental impurities.

A method for providing a wear interface surface on a substrate comprisesplacing a surface of a substrate into a plating bath including silvercations (Ag²⁺) and antimony cations (Sb³⁺ and Sb⁵⁺). A first platingcurrent pulse is repeatedly applied through the plating bath to reduce aportion of the silver cations (Ag²⁺) and the antimony cations (Sb³⁺ andSb⁵⁺). The reduced cations form a wear interface surface layer on thesubstrate having a chemical composition including between about 0.005 wt% and about 0.050 wt % of antimony (Sb), with the balance silver (Ag)and incidental impurities.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 schematically illustrates an example gas turbine engine.

FIG. 2 is a diagrammatic view of an example epicyclic gear system.

FIG. 3 is a schematic cross-sectional view through a portion of theexample epicyclic gear system.

FIG. 4 is a chart describing a process for coating an article such as asurface of a gear for an epicyclic gear system.

DETAILED DESCRIPTION

FIG. 1 schematically illustrates an example gas turbine engine 20 thatincludes fan section 22, compressor section 24, combustor section 26 andturbine section 28. Alternative engines might include an augmentersection (not shown) among other systems or features. Fan section 22drives air along bypass flow path B while compressor section 24 drawsair in along core flow path C where air is compressed and communicatedto combustor section 26. In combustor section 26, air is mixed with fueland ignited to generate a high pressure exhaust gas stream that expandsthrough turbine section 28 where energy is extracted and utilized todrive fan section 22 and compressor section 24.

Although the disclosed non-limiting embodiment depicts a turbofan gasturbine engine, it should be understood that the concepts describedherein are not limited to use with turbofans as the teachings may beapplied to other types of turbine engines; for example a turbine engineincluding a three-spool architecture in which three spoolsconcentrically rotate about a common axis, and where a low spool enablesa low pressure turbine to drive a fan directly, or via a gearbox, anintermediate spool that enables an intermediate pressure turbine todrive an intermediate compressor of the compressor section, and a highspool that enables a high pressure turbine to drive a high pressurecompressor of the compressor section.

Engine 20 generally includes low speed spool 30 and high speed spool 32mounted for rotation about an engine central longitudinal axis Arelative to an engine static structure 36 via several bearing systems38. Bearing systems 38 can each include one or more journal bearingswith a coated lubricant surface. It should be understood that variousbearing systems 38 at various locations may alternatively oradditionally be provided.

Low speed spool 30 generally includes inner shaft 40 that connects fan42 and low pressure (or first) compressor section 44 to low pressure (orfirst) turbine section 46. Inner shaft 40 drives fan 42 directly, orthrough a speed change device, such as geared architecture 48, to drivefan 42 (via fan shaft 64) at a lower speed than low speed spool 30.High-speed spool 32 includes outer shaft 50 that interconnects highpressure (or second) compressor section 52 and high pressure (or second)turbine section 54. Inner shaft 40 and outer shaft 50 are concentric androtate via bearing systems 38 about engine central longitudinal axis A.

Combustor 56 is arranged between high pressure compressor 52 and highpressure turbine 54. In one example, high pressure turbine 54 includesat least two stages to provide a double stage high pressure turbine 54.In another example, high pressure turbine 54 includes only a singlestage. As used herein, a “high pressure” compressor or turbineexperiences a higher pressure than a corresponding “low pressure”compressor or turbine.

The example low pressure turbine 46 has a pressure ratio that is greaterthan about 5. The pressure ratio of the example low pressure turbine 46is measured prior to an inlet of low pressure turbine 46 as related tothe pressure measured at the outlet of low pressure turbine 46 prior toan exhaust nozzle.

Mid-turbine frame 58 of engine static structure 36 is arranged generallybetween high pressure turbine 54 and low pressure turbine 46.Mid-turbine frame 58 further supports bearing systems 38 in turbinesection 28 as well as setting airflow entering low pressure turbine 46.

The core airflow C is compressed by low pressure compressor 44 then byhigh pressure compressor 52 mixed with fuel and ignited in combustor 56to produce high speed exhaust gases that are then expanded through highpressure turbine 54 and low pressure turbine 46. Mid-turbine frame 58includes vanes 60, which are in the core airflow path and function as aninlet guide vane for low pressure turbine 46. Utilizing vane 60 ofmid-turbine frame 58 as the inlet guide vane for low pressure turbine 46decreases the length of low pressure turbine 46 without increasing theaxial length of mid-turbine frame 58. Reducing or eliminating the numberof vanes in low pressure turbine 46 shortens the axial length of turbinesection 28. Thus, the compactness of gas turbine engine 20 is increasedand a higher power density may be achieved.

The disclosed gas turbine engine 20 in one example is a high-bypassgeared aircraft engine. In a further example, gas turbine engine 20includes a bypass ratio greater than about six (6), with an exampleembodiment being greater than about ten (10). The example gearedarchitecture 48 is an epicyclical gear train, such as a planetary gearsystem, star gear system or other known gear system, with a gearreduction ratio of greater than about 2.3. An example epicyclical geartrain with journal bearings is shown in subsequent figures.

In one disclosed embodiment, gas turbine engine 20 includes a bypassratio greater than about ten (10:1) and the fan diameter issignificantly larger than an outer diameter of low pressure compressor44. It should be understood, however, that the above parameters are onlyexemplary of one embodiment of a gas turbine engine including a gearedarchitecture and that the present disclosure is applicable to other gasturbine engines.

A significant amount of thrust is provided by bypass flow B due to thehigh bypass ratio. Fan section 22 of engine 20 is designed for aparticular flight condition—typically cruise at about 0.8 Mach and about35,000 feet. The flight condition of 0.8 Mach and 35,000 ft., with theengine at its best fuel consumption—also known as “bucket cruise ThrustSpecific Fuel Consumption (‘TSFC’)”—is an industry standard parameter ofpound-mass (lb_(m)) of fuel per hour being burned divided by pound-force(lb_(f)) of thrust the engine produces at that minimum point.

“Low fan pressure ratio” is the pressure ratio across the fan bladealone, without a Fan Exit Guide Vane (“FEGV”) system. The low fanpressure ratio as disclosed herein according to one non-limitingembodiment is less than about 1.50. In another non-limiting embodimentthe low fan pressure ratio is less than about 1.45.

“Low corrected fan tip speed” is the actual fan tip speed in ft/secdivided by an industry standard temperature correction of [(T_(ram)°R)/518.7]^(0.5). The “Low corrected fan tip speed”, as disclosed hereinaccording to one non-limiting embodiment, is less than about 1150ft/second.

The example gas turbine engine includes fan 42 that comprises in onenon-limiting embodiment less than about 26 fan blades. In anothernon-limiting embodiment, fan section 22 includes less than about 20 fanblades. Moreover, in one disclosed embodiment low pressure turbine 46includes no more than about 6 turbine rotors schematically indicated at34. In another non-limiting example embodiment low pressure turbine 46includes about 3 turbine rotors. A ratio between number of fan blades 42and the number of low pressure turbine rotors is between about 3.3 andabout 8.6. The example low pressure turbine 46 provides the drivingpower to rotate fan section 22 and therefore the relationship betweenthe number of turbine rotors 34 in low pressure turbine 46 and number ofblades 42 in fan section 22 disclose an example gas turbine engine 20with increased power transfer efficiency.

FIG. 2 shows an example epicyclic gear train 48, and also includes sungear 70, ring gear 72, star gears 74, gear carrier 76, journal bearings78, oil baffles 80, journal bearing outer interface surfaces 82, stargear inner interface surfaces 84, radial supply passages 86, anddistribution recesses 88.

In one example, geared architecture 48 is an epicyclic gear train with astationary star gear carrier and rotatable ring gear. Epicyclic gearsystems are complex mechanisms for reducing or increasing rotationalspeeds between two rotating shafts or rotors, such as between a lowspeed engine shaft and a fan drive shaft. The compactness of epicyclicgear trains makes them appealing for use in aircraft engines, but forcesand torque transferred through the gear train place tremendous stresseson the components, making them susceptible to breakage and wear.Imperfect alignment of longitudinal gear axes with the input shaftnecessitates increased amounts of lubrication to form an adequate filmthickness between each journal bearing and interfacing gears than wouldotherwise be necessary and reduce the amount of wear experiencedparticularly by the journal bearing and interfacing gears. Surfaces ofthe gears interfacing with journal bearings can be provided with ahardened silver-based coating or interface layer to provide a balance oflubrication, reduced friction, strength, and low cost as describedbelow.

Here, sun gear 70 is rotatably mounted to inner (low pressure) shaft 40(shown in FIG. 3). Fan shaft 64 (also shown in FIG. 3) is driven at alower speed than inner shaft 40 via ring gear 72, which turns fan 42(shown in FIG. 1). Star gears 74 include a plurality ofcircumferentially distributed gear teeth, and are enmeshed between sungear 70 and ring gear 72 such that star gears 74 rotate when sun gear 70rotates. Star gears 74 can include a gear body rotatably mounted onstationary gear carrier 76 by stationary journal bearings 78. When lowspeed spool 30 (shown in FIG. 1) rotates, epicyclic gear train 48therefore causes the fan to rotate at a slower rotational velocity thanthat of low speed spool 30, but in the opposite direction.

In an alternative embodiment, geared architecture 48 may be an epicyclicgear train configured with a rotatable star gear carrier 76 and a fixedring gear 72. This is sometimes called a planetary gear system. In thisalternative configuration, star or “planet” gears 74 are rotatablymounted on gear carrier 76 by journal bearings 78. Baffles or spray bars80 can be provided to help distribute lubricant through the interfacinggears. Star gears 74 mesh with sun gear 70 and mechanically groundedring gear 72. Input and output shafts (not shown) extend from sun gear70 and star gear carrier 76 respectively. During operation, the inputshaft, such as low speed shaft 40, rotatably drives sun gear 70, therebydriving star gears 74 and causing them to orbit sun gear 70 in themanner of a planet, which turns the gear carrier and the output shaft inthe same direction as the input shaft. The operation of similar examplesof epicyclic gear systems and lubrication systems for epicyclic gearsystems are further detailed in commonly assigned U.S. Pat. Nos.6,223,616 and 5,102,379, which are herein incorporated by reference.

In this example, each journal bearing 78 includes outer surface 82 whichinterfaces with respective star gear inner surface 84. Lubricant flowsthrough radial supply passages 86 into distribution recess 88 to form aload supporting lubricant film between journal bearing 78 and star gear74. The lubricant film is discharged from axial extremities of thebearing interface, most of which is directed into the sun/star mesh,aided by nearby baffles 80. The directed lubricant cools and lubricatesthe sun and star gear teeth and then is expelled from the sun/star mesh.The adjacent baffle 80 then guides substantially all of the expelledlubricant radially outwardly into the star/ring mesh before beingejected and centrifugally channeled away from epicyclic gear system 48.In one embodiment, the flow rate of lubricant provides journal bearinginterface surface 82 with a minimum lubricant film thickness of betweenabout 2.5 μm (about 100 micro inches) and 51 μm (about 2000 microinches).

Star gear inner surface 84 is worn by journal bearing outer interfacesurface 82, such that star gear inner surface 84 conforms to outerinterface surface 82 for controlling friction therebetween. Journalbearing outer interface surface 82 may optionally be finished to achievea fine surface roughness in order to minimize uneven wear on the softerstar gear inner surface 84. One suitable, non-limiting example of afinished journal bearing interface surface for an epicyclic gear systemis described in commonly assigned U.S. Pat. No. 8,172,716, which isherein incorporated by reference.

Star gear inner surface 84 can include a wear interface layer disposedover a surface of star gear 74 such as an inner diameter surfaceconfigured to face journal bearing 78. The wear interface layer can beplated directly onto star gear 74. Alternatively, star gear innersurface 84 can be plated onto a separate replaceable liner fittingannularly between journal bearing 78 and star gear 74. In any case,inner surface 84 includes a plated wear interface layer comprising asilver alloy. The interface layer can be pulse-plated by periodicallyapplying plating current pulses through a silver plating bath havingsmall amounts of antimony. This combination of pulse-plating voltage andcontrolling antimony composition of the interface layer can cooperate toenhance grain dimension control and hardness properties as describedbelow.

FIG. 3 shows a cross-section of engine 20 proximate epicyclic gearsystem 48. FIG. 3 also includes fan shaft 64 sun gear 70, ring gear 72,star gears 74, gear carrier 76, journal bearings 78, journal bearingouter interface surfaces 82, star gear inner interface surfaces 84,radial supply passage 86, distribution recess 88, gear carrier faces90A, 90B, end caps 92, lubricant feed tube 94, manifold 96, and axialsupply passage 98.

As described previously, star gear carrier 76 is stationarily mountedwithin gas turbine engine 20 to at least one non-rotating engine casewall (not shown) disposed radially outward from epicyclic gear system48. Carrier 76 has two generally interfacing faces 90A, 90B whichsupport the ends of stationary journal bearing 78. In the exampleembodiment shown in FIGS. 2 and 3, stationary journal bearing 78 ispositioned inside of rotatable star gear 74. End caps 92 are welded orotherwise affixed to journal bearing 78 and press fit into carrier 76 toprovide support for journal bearing 78. Fasteners extend through endcaps 92 and connect to carrier 76 to act as an anti-rotation feature tokeep journal bearing 78 stationary. Lubricant feed tube 94 feedspressurized lubricant to manifold 96, which is fluidly connected tojournal bearing 78 via axial supply passage 98 and radial supply passage86.

Main body portions of star gears 74 and journal bearings 78 aretypically made of steel. Commonly used steel grades includecase-hardenable AMS 6265 and AMS 6308. AMS 6265 is a nickel-chromiumbased steel. AMS 6308 includes molybdenum and vanadium to increasetoughness. In certain embodiments, journal bearing outer interfacesurfaces 82 are carburized, then smoothed or super-finished to removelarger asperities and achieve an amorphous surface roughness. Whilesofter than journal bearing outer interface surface 82, star gear innersurfaces 84 should have sufficient hardness and resilience to withstanda damaging combination of unit loading and linear sliding velocity whichmay exceed about 20 MPa (about 2900 psig), and about 50 msec (about 165ft/sec) respectively.

Star gear inner surfaces 84 can include a low-friction journal interfacesurface layer having a chemical composition between about 0.005 wt % andabout 0.050 wt % of antimony (Sb), with the balance silver (Ag) andincidental impurities. In certain embodiments, the interface layerincludes between about 0.010 wt % Sb and about 0.035 wt % Sb. In certainof those embodiments, the interface layer includes between about 0.015wt % Sb and about 0.025 wt % Sb.

Previous star gear interfaces have been provided with a wear interfacecoating or liner comprising a low-friction copper-lead alloy. However,the process to make such a coating with the correct composition andmicrostructure is complex, requires specialized equipment, and is thusexpensive and difficult to scale up. In contrast, silver coatingmaterials and processes are much simpler to handle and use, and silveris readily electroplated onto a variety of substrates. However, previoussilver coatings do not possess the hardness and resiliency required inharsh operating environments, such as for an interface surfacecontacting a journal bearing.

In substantially pure silver microstructures, small amounts of antimonyoperate as a grain dimension reducer. Reducing silver grain sizeeffectively increases the hardness, strength, and resiliency of theapplied silver while maintaining a low frictional coefficient for use asa wear interface surface layer. Grain dimension of the applied wearinterface layer can be further reduced by control ing the electroplatingprocess with pulsed plating voltages as described below. In certainembodiments, the silver interface layer has a microstructure with anaverage grain dimension of less than about 10 nm. In certain of thoseembodiments, the microstructure has an average grain dimension of lessthan about 5 nm. Depending on the exact process parameters, the wearinterface layer includes a hardness value measuring at least about 150on the Vickers scale. This hardness value is comparable to thepreviously described copper-lead alloy and larger than previously knownsilver-based wear interfaces. To achieve a silver-based wear interfacelayer with some or all of these properties, the wear interface surfacecan be pulse-plated from an Ag/Sb plating bath onto a surface of asubstrate. The substrate may be an article such as star gear 74 or ontoa separate liner as described above. Examples of pulse-plating aredescribed with respect to FIG. 4.

While the example wear interface surface is described with reference tojournal bearing surfaces for epicyclic gears, it will be appreciatedthat the described subject matter can be readily adapted to othersilver-based coating processes and articles. For example, the journalbearing and star gear substrates were previously described as steelalloys. It will be recognized that the metal alloy substrate canalternatively be a number of other substrates such as a superalloycomprising nickel or cobalt.

FIG. 4 is a flow chart depicting steps of example method 100 forproviding a wear interface surface on an article. The method can be usedto provide one or more wear interface surface layers on a rotatablearticle such as a gear element that is configured to interface androtate about a journal bearing. Step 102 describes placing a substrateinto a silver-based electroplating bath. The bath includes silvercations (Ag²⁺) and antimony cations (Sb³⁺ and/or Sb⁵⁺). Silver cations(Ag²⁺) can be provided by any suitable ionic composition such as but notlimited to silver halide salts. Antimony cations (Sb³⁺ and/or Sb⁵⁺) canbe added to an otherwise standard silver plating bath via commerciallyavailable silver brightening additives, examples of which includehydrates of antimony-containing alkali metal salts and/or ammoniumsalts. One suitable, non-limiting example of an antimony additive ispotassium antimonyl tartrate. Generally, the relative ratio of silverand antimony cations in the plating bath will be similar to the desiredcomposition in the finished interface. However, the exact additive andcomposition of the plating bath will vary based on the processconditions.

Step 104 includes repeatedly applying a first plating current pulsethrough the electroplating bath to reduce and deposit silver cations(Ag²⁺) and the antimony cations (Sb³⁺ and/or Sb⁵⁺) from the plating bathonto a surface of the substrate. Step 104 can be performed, for example,by applying discrete electric pulses through the plating bath using anysuitable control apparatus. Repeated pulses may each be applied for asubstantially constant first time duration, and separated by asubstantially constant second time duration. The first time duration,which may be less than 1.0 millisecond (ms), can optionally be equal tothe second time duration.

In certain of these embodiments, the first time duration of each of thefirst plating pulses can be less than about 0.5 ms. In certain of theseembodiments, the applied plating voltage and current are effectivelyzero between pulses. In one example, the first nonzero plating pulse isapplied for a first time duration of about 0.1 ms with a 0.1 ms secondtime duration between pulses, resulting in an overall plating duty cycleof the first nonzero plating voltage being at least about 50%.

Step 106 shows an optional step of periodically applying a secondplating current for a second time duration. This may be the second timeduration between the first nonzero plating voltages of step 104. Incertain embodiments, a polarity of the second plating current can be thesame as a polarity of the first plating current, but with a differentmagnitude. Alternatively, the second plating current can have adifferent voltage and/or an opposite polarity as compared to the firstplating current. In another example embodiment, the first time durationof the first plating current pulse about 0.2 ms and the second timeduration between first plating pulses is about 0.4 ms. Second currentpulses may be applied during some or all of the 0.4 ms second timeduration.

In combination with the alloy composition, pulse plating results in asilver-based wear interface surface layer with repeatable nanometerscale grain sizes and increased hardness properties. The resultingpulse-plated wear interface surface has between about 0.005 wt % andabout 0.050 wt % of antimony (Sb), with the balance silver (Ag) andincidental impurities. In certain embodiments the resulting wearinterface surface has between about 0.010 wt % and about 0.035 wt % ofantimony (Sb). In certain of those embodiments, the resulting wearinterface surface has between about 0.015 wt % and about 0.025 wt % ofantimony (Sb).

It was found that adding small amounts of antimony to otherwisesubstantially pure silver, in combination with the pulse plating processcan result in a hardened low-friction silver layer with controlled graindimensions. The combined effects of antimony composition withsub-millisecond pulse plating has been found to provide a simple silverplating process with tight control and repeatability of nanometer-scalegrains and high hardness properties, as compared to either factor alone.As noted above, embodiments of the process can result in a wearinterface with a hardened silver microstructure having an average graindimension of less than about 10 nm. In certain embodiments, theresulting microstructure can have an average grain dimension of lessthan about 5 nm. Resulting wear interface surface layers can have ahardness value measuring at least about 150 on the Vickers scale.

While the invention has been described with reference to an exemplaryembodiment(s), it will be understood by those skilled in the art thatvarious changes may be made and equivalents may be substituted forelements thereof without departing from the scope of the invention. Inaddition, many modifications may be made to adapt a particular situationor material to the teachings of the invention without departing from theessential scope thereof. Therefore, it is intended that the inventionnot be limited to the particular embodiment(s) disclosed, but that theinvention will include all embodiments falling within the scope of theappended claims.

Discussion of Possible Embodiments

The following are non-exclusive descriptions of possible embodiments ofthe present disclosure.

An article comprises a metal alloy substrate and a plated wear interfacelayer disposed over a surface of the metal alloy substrate. The platedwear interface layer has a chemical composition including between about0.005 wt % and about 0.050 wt % of antimony (Sb), and the balance silver(Ag) and incidental impurities.

The article of the preceding paragraph can optionally include,additionally and/or alternatively, any one or more of the followingfeatures, configurations and/or additional components:

An article according to an exemplary embodiment of this disclosure,among other possible things, includes a metal alloy substrate with aplated wear interface layer disposed over a surface of the metal alloysubstrate. The wear interface layer has a chemical composition includingbetween about 0.005 wt % and about 0.050 wt % of antimony (Sb), and thebalance silver (Ag) and incidental impurities.

A further embodiment of the foregoing article, wherein the wearinterface layer additionally and/or alternatively includes amicrostructure having an average grain dimension of less than about 10nm.

A further embodiment of any of the foregoing articles, wherein themicrostructure additionally and/or alternatively has an average graindimension of less than about 5 nm.

A further embodiment of any of the foregoing articles, wherein the wearinterface layer additionally and/or alternatively includes a hardnessvalue measuring at least about 150 on the Vickers scale.

A further embodiment of any of the foregoing articles, wherein the metalalloy substrate additionally and/or alternatively comprisescase-hardenable steel.

A further embodiment of any of the foregoing articles, wherein the wearinterface layer additionally and/or alternatively is an inner surface ofthe article and is configured to rotate about a journal bearing.

A further embodiment of any of the foregoing articles, wherein thearticle is a component for an epicyclic gear system.

A further embodiment of any of the foregoing articles, wherein thechemical composition additionally and/or alternatively includes betweenabout 0.015 wt % and about 0.025 wt % of antimony (Sb).

A gear element comprises a gear body, a plurality of gear teethdistributed circumferentially around the gear body, and a plated wearinterface layer disposed over an inwardly facing gear surface.

The gear element of the preceding paragraph can optionally include,additionally and/or alternatively, any one or more of the followingfeatures, configurations and/or additional components:

A gear element according to an exemplary embodiment of this disclosure,among other possible things, includes a gear body, a plurality of gearteeth distributed circumferentially around the gear body, and a platedwear interface layer disposed over an inwardly facing gear surface. Theplated wear interface layer has a chemical composition including betweenabout 0.005 wt % and about 0.050 wt % of antimony (Sb), with the balancesilver (Ag) and incidental impurities.

A further embodiment of the foregoing gear element, wherein the chemicalcomposition additionally and/or alternatively includes between about0.010 wt % and about 0.035 wt % of antimony (Sb).

A further embodiment of any of the foregoing gear elements, wherein thechemical composition additionally and/or alternatively includes betweenabout 0.015 wt % and about 0.025 wt % of antimony (Sb).

A further embodiment of any of the foregoing gear elements, wherein thebearing interface coating layer additionally and/or alternativelyincludes a microstructure having an average grain dimension of less thanabout 10 nm, and a hardness value measuring at least about 150 on theVickers scale.

A further embodiment of any of the foregoing gear elements, wherein thegear body additionally and/or alternatively comprises case-hardenablesteel.

A further embodiment of any of the foregoing gear elements, wherein thegear body additionally and/or alternatively is either a star gear or aplanetary gear for an epicyclic gear system.

A further embodiment of any of the foregoing gear elements, wherein theepicyclic gear system is a fan drive gear system for a gas turbineengine.

A method for coating an article comprises placing a surface of asubstrate into a plating bath including silver cations (Ag²⁺) andantimony cations (Sb³⁺ and Sb⁵⁺) and repeatedly applying a first platingcurrent pulse through the plating bath.

The method of the preceding paragraph can optionally include,additionally and/or alternatively, any one or more of the followingfeatures, configurations and/or additional components:

A method for coating a substrate according to an exemplary embodiment ofthis disclosure, among other possible things, includes placing a surfaceof the substrate into a plating bath including silver cations (Ag²⁺) andantimony cations (Sb³⁺ and Sb⁵⁺) and repeatedly applying a first platingcurrent pulse through the plating bath to reduce a portion of the silvercations (Ag²⁺) and the antimony cations (Sb³⁺ and Sb⁵⁺). The reducedcations form a coating layer having a chemical composition includingbetween about 0.005 wt % and about 0.050 wt % of antimony metal (Sb),with the balance silver (Ag) metal and incidental impurities.

A further embodiment of the foregoing method, wherein additionallyand/or alternatively, the repeated first pulses are each applied for asubstantially constant first time duration.

A further embodiment of any of the foregoing methods, whereinadditionally and/or alternatively, the first time duration is less thanabout 1.0 millisecond (ms).

A further embodiment of any of the foregoing methods, whereinadditionally and/or alternatively, a second plating current pulse isrepeatedly applies through the plating bath, with each second currentpulse applied for a second time duration.

A further embodiment of any of the foregoing methods, whereinadditionally and/or alternatively, the first time duration issubstantially equal to the second time duration.

A further embodiment of any of the foregoing methods, whereinadditionally and/or alternatively, the first plating current pulse isapplied with a first polarity, and the second plating current pulse isapplied with a second polarity, the second polarity being opposite thefirst polarity.

A further embodiment of any of the foregoing methods, whereinadditionally and/or alternatively, the resulting coating includes amicrostructure having an average grain dimension of less than about 10nm.

A further embodiment of any of the foregoing methods, whereinadditionally and/or alternatively, the resulting coating includes ahardness value measuring at least about 150 on the Vickers scale.

The invention claimed is:
 1. A method for providing a wear interfacesurface on a substrate, the method comprising: placing a surface of thesubstrate into a plating bath including silver cations (Ag²⁺) andantimony cations (Sb³⁺ and Sb⁵⁺); repeatedly applying a first platingcurrent pulse through the plating bath to reduce a portion of the silvercations (Ag²⁺) and the antimony cations (Sb³⁺ and Sb⁵⁺), the reducedcations forming a wear interface surface layer on the substrate having achemical composition including between about 0.005 wt % and about 0.050wt % of antimony metal (Sb), with the balance silver (Ag) metal andincidental impurities.
 2. The method of claim 1, wherein each firstplating current pulse is applied for a substantially constant first timeduration.
 3. The method of claim 2, wherein the first time duration isless than about 1.0 millisecond (ms).
 4. The method of claim 2, furthercomprising: repeatedly applying a second plating current pulse throughthe plating bath, each second plating current pulse applied for a secondtime duration.
 5. The method of claim 4, wherein the first time durationis substantially equal to the second time duration.
 6. The method ofclaim 4, wherein the first plating current pulse is applied with a firstpolarity, and the second plating current pulse is applied with a secondpolarity, the second polarity being opposite the first polarity.
 7. Themethod of claim 1, wherein the resulting coating includes amicrostructure having an average grain dimension of less than about 10nm.
 8. The method of claim 1, wherein the resulting coating includes ahardness value measuring at least about 150 on the Vickers scale.
 9. Themethod of claim 1, wherein at least the surface of the substrate placedinto the plating bath comprises case-hardenable steel.
 10. The method ofclaim 1, wherein the surface of the substrate placed into the platingbath is an inner surface of the substrate and is configured to rotateabout a journal bearing contacting the wear interface layer.
 11. Themethod of claim 1, wherein the substrate is a component for an epicyclicgear system.
 12. A method comprising: providing a gear element whichincludes a plurality of circumferentially distributed gear teeth and agear contact surface configured for contact with a journal bearing; andplacing at least the gear contact surface into a plating bath includingsilver cations (Ag²⁺ ) and antimony cations (Sb³⁺ and Sb⁵⁺); repeatedlyapplying a first plating current pulse through the plating bath toreduce a portion of the silver cations (Ag²⁺ ) and the antimony cations(Sb³⁺ and Sb⁵⁺), the reduced cations forming a wear interface surfacelayer on at least the gear contact surface, the wear interface surfacelayer having a chemical composition including between about 0.005 wt %and about 0.050 wt % of antimony metal (Sb), with the balance silver(Ag) metal and incidental impurities.
 13. The method of claim 12,wherein the chemical composition includes between about 0.010 wt % andabout 0.035 wt % of antimony (Sb).
 14. The method of claim 12, whereinthe wear interface surface layer includes a microstructure having anaverage grain dimension of less than about 10 nm, and a hardness valuemeasuring at least about 150 on the Vickers scale.
 15. The method ofclaim 12, wherein the gear element is either a star gear or a planetarygear for an epicyclic gear system.
 16. The method of claim 12, whereineach first plating current pulse is applied for a substantially constantfirst time duration.
 17. The method of claim 16, wherein the first timeduration is less than about 1.0 millisecond (ms).
 18. The method ofclaim 16, further comprising: repeatedly applying a second platingcurrent pulse through the plating bath, each second plating currentpulse applied for a second time duration.
 19. The method of claim 18,wherein the first time duration is substantially equal to the secondtime duration.
 20. The method of claim 18, wherein the first platingcurrent pulse is applied with a first polarity, and the second platingcurrent pulse is applied with a second polarity, the second polaritybeing opposite the first polarity.